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authorAndy Chiu <andy.chiu@sifive.com>2024-01-15 05:59:24 +0000
committerPalmer Dabbelt <palmer@rivosinc.com>2024-01-16 07:13:57 -0800
commitc2a658d419246108c9bf065ec347355de5ba8a05 (patch)
tree01afac13dfa6c595dd5154b3f45a2a6fe929f728 /arch/riscv/lib
parent7df56cbc27e4239807b5d8860f79a7350d63a741 (diff)
riscv: lib: vectorize copy_to_user/copy_from_user
This patch utilizes Vector to perform copy_to_user/copy_from_user. If Vector is available and the size of copy is large enough for Vector to perform better than scalar, then direct the kernel to do Vector copies for userspace. Though the best programming practice for users is to reduce the copy, this provides a faster variant when copies are inevitable. The optimal size for using Vector, copy_to_user_thres, is only a heuristic for now. We can add DT parsing if people feel the need of customizing it. The exception fixup code of the __asm_vector_usercopy must fallback to the scalar one because accessing user pages might fault, and must be sleepable. Current kernel-mode Vector does not allow tasks to be preemptible, so we must disactivate Vector and perform a scalar fallback in such case. The original implementation of Vector operations comes from https://github.com/sifive/sifive-libc, which we agree to contribute to Linux kernel. Co-developed-by: Jerry Shih <jerry.shih@sifive.com> Signed-off-by: Jerry Shih <jerry.shih@sifive.com> Co-developed-by: Nick Knight <nick.knight@sifive.com> Signed-off-by: Nick Knight <nick.knight@sifive.com> Suggested-by: Guo Ren <guoren@kernel.org> Signed-off-by: Andy Chiu <andy.chiu@sifive.com> Tested-by: Björn Töpel <bjorn@rivosinc.com> Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> Link: https://lore.kernel.org/r/20240115055929.4736-6-andy.chiu@sifive.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'arch/riscv/lib')
-rw-r--r--arch/riscv/lib/Makefile6
-rw-r--r--arch/riscv/lib/riscv_v_helpers.c45
-rw-r--r--arch/riscv/lib/uaccess.S10
-rw-r--r--arch/riscv/lib/uaccess_vector.S53
4 files changed, 113 insertions, 1 deletions
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 494f9cd1a00c..c8a6787d5827 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -6,9 +6,13 @@ lib-y += memmove.o
lib-y += strcmp.o
lib-y += strlen.o
lib-y += strncmp.o
-lib-$(CONFIG_MMU) += uaccess.o
+ifeq ($(CONFIG_MMU), y)
+lib-y += uaccess.o
+lib-$(CONFIG_RISCV_ISA_V) += uaccess_vector.o
+endif
lib-$(CONFIG_64BIT) += tishift.o
lib-$(CONFIG_RISCV_ISA_ZICBOZ) += clear_page.o
obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
lib-$(CONFIG_RISCV_ISA_V) += xor.o
+lib-$(CONFIG_RISCV_ISA_V) += riscv_v_helpers.o
diff --git a/arch/riscv/lib/riscv_v_helpers.c b/arch/riscv/lib/riscv_v_helpers.c
new file mode 100644
index 000000000000..be38a93cedae
--- /dev/null
+++ b/arch/riscv/lib/riscv_v_helpers.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2023 SiFive
+ * Author: Andy Chiu <andy.chiu@sifive.com>
+ */
+#include <linux/linkage.h>
+#include <asm/asm.h>
+
+#include <asm/vector.h>
+#include <asm/simd.h>
+
+#ifdef CONFIG_MMU
+#include <asm/asm-prototypes.h>
+#endif
+
+#ifdef CONFIG_MMU
+size_t riscv_v_usercopy_threshold = CONFIG_RISCV_ISA_V_UCOPY_THRESHOLD;
+int __asm_vector_usercopy(void *dst, void *src, size_t n);
+int fallback_scalar_usercopy(void *dst, void *src, size_t n);
+asmlinkage int enter_vector_usercopy(void *dst, void *src, size_t n)
+{
+ size_t remain, copied;
+
+ /* skip has_vector() check because it has been done by the asm */
+ if (!may_use_simd())
+ goto fallback;
+
+ kernel_vector_begin();
+ remain = __asm_vector_usercopy(dst, src, n);
+ kernel_vector_end();
+
+ if (remain) {
+ copied = n - remain;
+ dst += copied;
+ src += copied;
+ n = remain;
+ goto fallback;
+ }
+
+ return remain;
+
+fallback:
+ return fallback_scalar_usercopy(dst, src, n);
+}
+#endif
diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
index 3ab438f30d13..a1e4a3c42925 100644
--- a/arch/riscv/lib/uaccess.S
+++ b/arch/riscv/lib/uaccess.S
@@ -3,6 +3,8 @@
#include <asm/asm.h>
#include <asm/asm-extable.h>
#include <asm/csr.h>
+#include <asm/hwcap.h>
+#include <asm/alternative-macros.h>
.macro fixup op reg addr lbl
100:
@@ -11,6 +13,13 @@
.endm
SYM_FUNC_START(__asm_copy_to_user)
+#ifdef CONFIG_RISCV_ISA_V
+ ALTERNATIVE("j fallback_scalar_usercopy", "nop", 0, RISCV_ISA_EXT_v, CONFIG_RISCV_ISA_V)
+ REG_L t0, riscv_v_usercopy_threshold
+ bltu a2, t0, fallback_scalar_usercopy
+ tail enter_vector_usercopy
+#endif
+SYM_FUNC_START(fallback_scalar_usercopy)
/* Enable access to user memory */
li t6, SR_SUM
@@ -181,6 +190,7 @@ SYM_FUNC_START(__asm_copy_to_user)
sub a0, t5, a0
ret
SYM_FUNC_END(__asm_copy_to_user)
+SYM_FUNC_END(fallback_scalar_usercopy)
EXPORT_SYMBOL(__asm_copy_to_user)
SYM_FUNC_ALIAS(__asm_copy_from_user, __asm_copy_to_user)
EXPORT_SYMBOL(__asm_copy_from_user)
diff --git a/arch/riscv/lib/uaccess_vector.S b/arch/riscv/lib/uaccess_vector.S
new file mode 100644
index 000000000000..51ab5588e9ff
--- /dev/null
+++ b/arch/riscv/lib/uaccess_vector.S
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+#include <asm-generic/export.h>
+#include <asm/asm.h>
+#include <asm/asm-extable.h>
+#include <asm/csr.h>
+
+#define pDst a0
+#define pSrc a1
+#define iNum a2
+
+#define iVL a3
+
+#define ELEM_LMUL_SETTING m8
+#define vData v0
+
+ .macro fixup op reg addr lbl
+100:
+ \op \reg, \addr
+ _asm_extable 100b, \lbl
+ .endm
+
+SYM_FUNC_START(__asm_vector_usercopy)
+ /* Enable access to user memory */
+ li t6, SR_SUM
+ csrs CSR_STATUS, t6
+
+loop:
+ vsetvli iVL, iNum, e8, ELEM_LMUL_SETTING, ta, ma
+ fixup vle8.v vData, (pSrc), 10f
+ sub iNum, iNum, iVL
+ add pSrc, pSrc, iVL
+ fixup vse8.v vData, (pDst), 11f
+ add pDst, pDst, iVL
+ bnez iNum, loop
+
+ /* Exception fixup for vector load is shared with normal exit */
+10:
+ /* Disable access to user memory */
+ csrc CSR_STATUS, t6
+ mv a0, iNum
+ ret
+
+ /* Exception fixup code for vector store. */
+11:
+ /* Undo the subtraction after vle8.v */
+ add iNum, iNum, iVL
+ /* Make sure the scalar fallback skip already processed bytes */
+ csrr t2, CSR_VSTART
+ sub iNum, iNum, t2
+ j 10b
+SYM_FUNC_END(__asm_vector_usercopy)